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From: Joe Greco <jgreco@brasil.moneng.mei.com>
Message-Id: <199602172100.PAA06868@brasil.moneng.mei.com>
Subject: Re: Web server locks up... but not quite. (?) (fwd)
To: bugs@freebsd.netcom.com (Mark Hittinger)
Date: Sat, 17 Feb 1996 15:00:13 -0600 (CST)
Cc: hackers@FreeBSD.ORG
In-Reply-To: <199602171548.JAA03588@freebsd.netcom.com> from "Mark Hittinger" at Feb 17, 96 09:48:33 am
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> Is the 4 gig drive a Seagate barracuda?    (yes for me, bt946c)
> 
> Do you run alias ip's for 'virtual web sites'?  (yes for me, a bunch)
> 
> What ethernet card do you run on the box?       (3c509 isa for me)
> 
> How large is your swap file?                   (256mb swap file)
> 
> The reason I ask these questions is that other boxes running the same rev
> of FreeBSD will not exhibit the problem at all.  I am trying to find the
> common thread.

For me, the box was a 486DX4/120 with IDE disk, no IP aliases, SMC Elite
8013, unknown swap file size, acting as a PPP terminal server.

The frequency of occurence was extremely low (I think twice in a six month
period).

> > I've seen similar hangs occasionally under both 2.0.5R and 2.1.0R and one
> > additional "thing" I've noticed is that processes that are completely
> > in-core appear to keep running (i.e. I had a "vmstat 1" running for a few
> > weeks and when the box I am thinking of locked up, the vmstat 1 was still
> > scrolling output, the box was ping-able, but any services that were not
> > entirely in-core or required other disk accesses were not available).
> > There is something to the "in-core" business because I have seen the same
> > box both continue to broadcast rwho and NOT broadcast rwho, presumably
> > determined by whether or not it was in-core..
> 
> I saw this behavior before 2.0.5, then it went away until about 3 weeks
> before 2.1R was cut.
> 
> I will see the following kinds of processes hang (unkillable)
> in "D+" state via ps.  Innd, Cern httpd, and ps.
> 
> Ps seems to have it happen a lot.  "ps -ax" will hang whereas simply "ps"
> will not.   When "ps -ax" hangs, who and top will run ok.

I wasn't lucky enough to have a runnable shell prompt.

> I am wondering if the "ps -ax" hangs are because it is trying to look at
> the swap space of another process which is hung and I don't realize it :-)
> This would imply some kind of deadlock condition for a page out on the
> swap space.

It's looking like that could well be the case, it is consistent with the
symptoms I had seen.

... Joe

-------------------------------------------------------------------------------
Joe Greco - Systems Administrator			      jgreco@ns.sol.net
Solaria Public Access UNIX - Milwaukee, WI			   414/546-7968